The present invention relates to the thermal flashing of carbonaceous materials. More specifically, the present invention relates to the thermal flashing of carbonaceous materials under conditions minimizing the destruction of flashed products.
Dwindling supplies of crude oil, particularly light oils containing small amounts of sulfur, nitrogen, metals and other contaminants, make it highly desirable that alternate sources of carbonaceous materials, such as oil shale, coals, lignites, tar sands, biomass and the like, heavier more highly contaminated crude oils and less desirable, normally solid fractions of crude oil be processed to produce more valuable liquid and gaseous fuels and feedstocks for production of chemicals and products thereof.
While some of the above-mentioned alternate sources of hydrocarbons, such as coal, lignite, biomass, etc. can be burned directly, such combustion is useful only for the production of heat, rather than more valuable products and, in most instances, the flue gases produced create serious pollution problems. Liquids of the nature of crude oil which can be processed to produce fuels and chemical feedstocks can be extracted from coal, lignite, oil shale and tar sands by solvent extraction. However, such solvent extraction is inefficient, and costly. In addition, direct burning of such oils is difficult and is subject to the same problems as burning the carbonaceous material directly, except that noncombustible solids have been removed. A large number of thermal processes have also been proposed for the production of liquids which can be upgraded to more valuable products, as well as directly useful fuels and chemical feedstocks. Such thermal processes are often classified as retorting when the source material contains substantial amounts of noncarbonaceous materials, such as oil shales and tar sands, or pyrolysis where the source material is relatively free of a noncarbonaceous material such as coal, lignite, normally solid hydrocarbons, biomass and the like. However, such terminology creates a distinction without substance since both involve the same physical and chemical transformations. Most widely researched and successful thermal techniques for the recovery of hydrocarbon materials from normally solid carbonaceous materials include strict thermal techniques to produce gases and liquids, the production of synthesis gas (about 50% hydrogen, 40% carbon monoxide, 3% carbon dioxide and 3% nitrogen) by heating in the presence of steam, generally referred to as steam reforming, heating in the presence of air and steam, generally referred to as the water gas reaction, and heating in the presence of hydrogen, generally referred to as hydropyrolysis or hydroretorting, to produce liquids and gases. Heat is supplied to such processes in one of four basic ways, namely, type I, in which heat is transferred through the wall of the vessel, type II, wherein a part of the carbonaceous material itself is burned in the reaction vessel, type III, wherein gases are heated externally of the reaction vessel, and type IV, wherein solids (often residual solids from the process itself) are heated externally of the reaction vessel. Such processes are also carried out in a variety of ways, including batch, semi-batch and continuous techniques as a fixed bed, a moving bed or fluidized bed and when contacting the solid material with a fluid either concurrent or countercurrent. All of these processes and the operating techniques generally involve the use of complex and expensive equipment, are complex multiple step techniques, are highly energy intensive and are over sensitive to variations in the conditions of operation. Additionally, substantial changes in technique and equipment are necessary in order to process different types of solid carbonaceous materials. Further, the generally utilized severe conditions of heat, pressure and/or residence time employed in such processes result in secondary decomposition in which liquids removed from the solid carbonaceous materials are decomposed to gaseous products suitable primarily for gaseous fuels and chemical feedstocks while sacrificing liquid products which can be burned directly or further processed into needed liquid fuels. While some of the more well developed processes of this character are close to being economically viable, are relatively efficient in removing extractable carbon and hydrogen and produce products requiring minimum further processing substantial improvements are still needed.